Personification given to mainly booze, and sometimes referring to other drugs. Generally used to refer to drugs when a person is feeling down and a person is saying it's what they need and/or use to feel better.

Guy 1: That sucks about your girlfriend leaving you for another guy after all your time together

Guy 2: Yeah, I'm gonna have a few appointments with Dr. Feelgood, even one tonight.

This is the name of the character in Motley Crue's Hit song Dr Feelgood. Dr Feelgood is a drug dealer that sells cocaine and other drugs to the mexican mob. HE is feared by police oficers and has them on his payroll. Since he distributes so much drugs the people on the streets refer to him as Dr feelgood since he is the one you go to get a fix. The song ends with Dr Feel good getting arrested.

He is the one they call Dr Feel Good he is the one who makes you feel alright!